Process for converting plastic into gases, liquid fuels and waxes by cracking

ABSTRACT

The present invention relates to a process for converting a mixture comprising plastic and at least one oxygenated compound into gases, liquid fuels and waxes by cracking. The process comprises a deoxygenation step and subsequently a cracking step during which the mixture is subjected to cracking conditions for obtaining a product stream containing said gases, liquid fuels and waxes.

This application claims priority to European application No. EP16306634.3 filed on Dec. 7, 2016, the whole content of this applicationbeing incorporated herein by reference for all purposes.

TECHNICAL FIELD

The present invention relates to a process for converting a mixturecomprising plastic and at least one oxygenated compound into gases,liquid fuels and waxes by cracking. The process comprises adeoxygenation step and subsequently a cracking step during which themixture is subjected to cracking conditions for obtaining a productstream containing said gases, liquid fuels and waxes.

PRIOR ART

In view of the increasing importance of polymers as substitutes forconventional materials of construction, such as glass, metal, paper andwood, the perceived need to safe non-renewable resources such aspetroleum and dwindling amounts of landfilled capacity available for thedisposal of waste products, considerable attention has been devoted inrecent years to the problem of recovering, reclaiming, recycling or insome way reusing waste plastic.

It has been proposed to pyrolyze or catalytically crack the wasteplastic so as to convert high molecular weight polymers into volatilecompounds having much lower molecular weight. The volatile compounds,depending on the process employed, can be either relatively high-boilingliquid hydrocarbons useful as fuel oils or fuel oil supplements orlight- to medium-boiling carbon atoms useful as gasoline-type fuels oras other chemicals. Furthermore, the volatile compounds can be or atleast can include waxes.

Cracking of a mixed waste plastic is a process well-known to the personskilled in the art. For example, U.S. Pat. No. 5,216,149 discloses amethod for controlling the pyrolysis of complex waste stream of plasticsto convert such stream into useful high-value monomers or otherchemicals, by identifying catalyst and temperature conditions thatpermit decomposition of a given polymer.

The known processes for plastic depolymerization by thermal or catalyticcracking usually leads to the formation of five main products that canbe categorized according to their carbon chain length, from shorter tolonger: gases, gasoline, diesel, kerosene and waxes (or HCO=Heavy CycleOil).

The present inventors found that available technologies have thedrawback that oxygenated compounds being present in the raw material arein most cases detrimental as they increase the oxygen content in theobtained products thereby lowering their quality. The production ofhigh-value products that have low oxygen content from mixturescomprising plastic and oxygenated compounds would therefore by desirable(Pavel T. Williams in “Waste treatment and disposal”, 2^(nd) ed., JohnWiley and Sons, Chichester, 2005, p 334).

A process for converting oxygenated hydrocarbons into hydrocarbons isdescribed in U.S. Pat. No. 4,308,411. This process starts from solidwaste, including cellulosic materials, from which an inorganic fractionis separated. The organic fraction is dried and then pyrolyzed at atemperature of from about 300° C. to about 800° C., such as 550° C. inthe examples. The thus obtained vapor comprising oxygenated hydrocarbonsis separated and subsequently the oxygenated hydrocarbons are contactedwith a crystalline aluminosilicate zeolite for conversion intohydrocarbons. While this process allows for the reduction of oxygenatedhydrocarbons, it has the drawback that the organic fraction of the solidwaste first has to be pyrolyzed at high temperature. At such hightemperature, the plastic in the solid waste also depolymerizes and thedepolymerization products can react with the oxygenized compoundsresulting in an undesired high oxygen content of the obtained gases,liquid fuels and waxes.

There is therefore still a need for further improving the cracking ofplastic, in particular for converting a mixture comprising plastic andat least one oxygenated compound into gases, liquid fuels and waxeshaving a low oxygen content.

BRIEF DESCRIPTION OF THE INVENTION

The present inventors now found that oxygenated compounds can be removedfrom a mixture comprising plastic and the oxygenated compounds at arather low temperature. Additionally, the inventors found that thedensity of the condensate of the gas stream obtained from the heatedmixture is a suitable marker for determining the end of thedeoxygenation process. At the beginning of the process, the density ofthe condensate is high. During deoxygenation the density of thecondensate decreases. At a certain density a substantial amount of theundesired oxygenated compound has been removed from the mixture so thatduring the subsequent cracking step a product stream containing gases,liquid fuels and waxes of high quality and low oxygen content isobtained.

DETAILED DESCRIPTION OF THE INVENTION

The present invention therefore relates to a process for converting amixture comprising plastic and at least one oxygenated compound intogases, liquid fuels and waxes by cracking, the process comprising:

-   -   a deoxygenation step which is conducted by heating the mixture        to a temperature of at least 200° C. for a period until the        condensate of the gas stream obtained from the heated mixture        has a density of about 0.94 g/cm³ or lower;    -   and subsequently to the deoxygenation step a cracking step        during which the mixture is subjected to cracking conditions for        obtaining a product stream containing said gases, liquid fuels        and waxes.

In the cracking of plastic several fractions of chemical compounds areobtained. Usually, there is a gas fraction containing light-weightchemical compounds with less than 5 carbon atoms. The gasoline fractioncontains compounds having a low boiling point of for example below 150°C. This fractions includes compounds having 5 to 9 carbon atoms. Thekerosene and diesel fraction has a higher boiling point of for example150° C. to 359° C. This fraction generally contains compounds having 10to 21 carbon atoms. The even higher-boiling fractions are generallydesignated as heavy cycle oil (or HCO) and waxes. In all thesefractions, the compounds are hydrocarbons which optionally compriseheteroatoms, such as N, O, etc. “Waxes” in the sense of the presentinvention therefore designate hydrocarbons which optionally containheteroatoms. In most cases, they are solid at room temperature (23° C.)and have a softening point of generally above 26° C. A definition of theobtained fractions is provided in the experimental section below.

A plastic is mostly constituted of a particular polymer and the plasticis generally named by this particular polymer. Preferably, a plasticcontains more than 25% by weight of its total weight of the particularpolymer, preferably more than 40% by weight and more preferably morethan 50% by weight. Other components in plastic are for exampleadditives, such as fillers, re-enforcers, processing aids, plasticizers,pigments, light stabilizers, lubricants, impact modifiers, antistaticagents, inks, antioxidants, etc. Generally, a plastic comprises morethan one additive.

Plastics used in the process of the present invention includepolyolefins and polystyrene, such as high-density polyethylene (HDPE),low-density polyethylene (LDPE), ethylene-propylene-diene monomer(EPDM), polypropylene (PP), and polystyrene (PS). Mixed plastics mostlyconstituted of polyolefin and/or polystyrene are preferred.

Other plastics, such as polyvinyl chloride, polyvinylidene chloride,polyethylene terephthalate, polyurethane (PU),acrylonitrile-butadiene-styrene (ABS), ethylene vinyl alcohol polymer(EVA), polyvinylacetate, polycarbonate, polyacrylate,polymethylmetacrylate (PMMA), nylon and fluorinated polymers are lessdesirable. If present in the plastic, they are preferably present in aminor amount of less than 50% by weight, preferably less than 30% byweight, more preferably less than 20% by weight, even more preferablyless than 10% by weight of the total weight of the dry weight plastic.

Preferably, the plastic comprises one or more thermoplastic polymers andis essentially free of thermosetting polymers. Essentially free in thisregard is intended to denote a content of thermosetting polymers of lessthan 15, preferably less than 10 and even more preferably less than 5%by weight of the plastic starting material.

The plastic used in the process of the present invention can be selectedamong:

-   -   single waste plastic, single virgin plastic on spec or off spec,        mixed waste plastic, rubber waste, organic waste, biomass or a        mixture thereof. Single plastic waste, single virgin plastic off        spec, mixed waste plastic, rubber waste or a mixture thereof are        preferred. Single virgin plastic off-spec, mixed waste plastic        or a mixture thereof particularly preferred. Mixed plastic waste        gives usually good results.

Prior to the process of the invention, the mixture can be pretreated bya physico-chemical process including one or more operations as sizereduction, grinding, shredding, screening, chipping, melt removal,foreign material removal, dust removal, drying, degassing, melting,solidifying and agglomerating.

Usually, waste plastic contains other non-desired components, namelyforeign materials such as glass, stone, metal, etc. Limited quantitiesof such unpyrolizable components as contaminant of the inlet rawmaterial are acceptable. For example, the mixture used in the process ofthe present invention may contain less than 50% by weight, preferablyless than 20% by weight, more preferably less than 10% by weight of thetotal weight of the dry mixture unpyrolizable components.

Additionally, waste plastic very often contains other non-desiredcomponents, mainly cellulosic base materials, such as wood, cardboard,paper, tissue, etc. These pyrolizable components are mostly oxygenatedcompounds, such as oxygenated hydrocarbons, which during cracking ofplastic result in an undesired increase in oxygen content of theobtained gases, liquid fuels and waxes.

“Oxygenated compounds” in the sense of the present invention are,however, not limited to organic compounds but may also include inorganiccompounds which comprise oxygen atoms being bound to other atoms butwhich are chemically not stable under the cracking conditions. H₂O isnot considered as an oxygenated compound in the sense of the presentinvention.

It was believed that these oxygenated compounds are difficult to removebecause pyrolysis of oxygenated compounds, such as cellulosic materials,as suggested in U.S. Pat. No. 4,308,411 requires high temperatures atwhich cracking of the plastic may occur.

The present inventors now surprisingly found that in a mixturecomprising plastic and at least one oxygenated compound the temperaturerequired for converting the oxygenated compound into gases is ratherlow. There remained, however, the problem that under specific conditionsalso plastics can be cracked at low temperatures. It was thereforenecessary to determine a parameter suitable for distinguishing betweenthe deoxygenation process during which the oxygenated compounds areremoved from the mixture and the cracking process during which theplastic is converted into the desired products. Upon furtherinvestigation, the present inventors found that the density of thecondensate of the gas stream obtained from the heated mixture is asuitable parameter to distinguish between the deoxygenation step and thecracking step.

The inventors found that during a batch operation at the beginning ofthe conversion of the mixture comprising plastic and oxygenatedcompounds, the density of the condensate of the gas stream obtained fromthe heated mixture is rather high. When the reaction proceeds, thedensity decreases. It was found that when the condensate reaches adensity of about 0.94 g/cm³, a considerable amount or even substantiallyall of the undesired oxygenated compounds has been removed from themixture. The thus remaining mixture comprises most of the plastic beingpresent in the initial mixture and a considerably reduced amount ofundesired oxygenated compounds. Thus, if the mixture remaining after thedeoxygenation step is subjected to cracking conditions, a product streamcontaining gases, liquid fuels and waxes of high quality in particularwith respect to reduced oxygen content is obtained. At the same time,only a small amount of the plastic being present in the initial mixtureis depolymerized during the deoxygenation step. Thus, the measurement ofthe density of the condensate of the gas stream obtained from the heatedmixture allows for an optimization not only of the quality of theobtained gases, liquid fuels and waxes but also of their yield.

In preferred embodiments of the present invention, the deoxygenationstep is conducted until the condensate of the gas stream obtained fromthe heated mixture has a density in the range of 0.90 g/cm³ to 0.93g/cm³, preferably in the range of 0.91 g/cm³ to 0.93 g/cm³, morepreferably in the range of 0.920 g/cm³ to 0.928 g/cm³, even morepreferably in the range of 0.923 g/cm³ to 0.927 g/cm³, and mostpreferably about 0.925 g/cm³.

In the context of the present invention, the “condensate of the gasstream obtained from the heated mixture” is to be understood as thefraction of gaseous products obtained from the mixture being heated toat least 200° C. which is obtained when cooling the hot gas stream to40° C. Those components of the gas stream which do not condense at 40°C. are discharged. The condensate is then further cooled to atemperature of 25° C. At this temperature the density of the condensateis measured. Possibly, the condensate may split into an aqueous fractionand an oil fraction. Therefore, the density of the condensate is definedas the ratio of the weight of the sample to the volume of the samplewithout taking into account any possible liquid phase split. Thismeasurement can be conducted by simply using the apparent weight andapparent volume of the “mixed” condensate.

For measuring the density of the condensate a certain volume of thecondensate is required. If the flow of condensate obtained during thedeoxygenation step is high enough, the density of the condensate can bemeasured continuously or at least semi-continuously. It can, however, bepreferred to collect a certain volume of the condensate before measuringits density. For example, in particular in a patch process, a suitablevolume can be selected relative to the amount of plastic in the startingmixture being introduced into the reactor. In this case, the volume canbe in the range of 0.1 to 250 cm³/kg of the plastic, preferably 0.15 to100 cm³/kg of the plastic, more preferably 0.2 to 20 cm³/kg of theplastic. In another embodiment a suitable volume can be in the range offor example 0.5 to 10 cm³, preferably 0.5 to 5 cm³, more preferably from0.5 to 4 cm³. The smaller the volume collected for measurement of thedensity the higher the precision in deciding when the deoxygenation stepends and the cracking step starts can be. Alternatively, the condensatecan be collected for a certain time before the density of the condensatecollected during this time is measured. The time interval during whichthe condensate is collected depends for example on the composition andamount of the mixture comprising the plastic and the oxygenatedcompound, the size of the reactor, the catalyst, the heating powder, theflow of the condensate, etc. and can be in the range of for example 1 to120 minutes, preferably 1 to 90 minutes, more preferably 1 to 60minutes, such as in the range of 2 to 30 minutes. Again, the shorter thetime interval during which the condensate is collected for themeasurement of its density, the higher is the precision in determiningthe end of the deoxygenation step and the beginning of the crackingstep.

Thus, during the deoxygenation step the obtained condensate is collectedeither for a certain period of time or until a certain volume isobtained. The density of the thus obtained condensate is measured and,if the density is above about 0.94 g/cm³, the deoxygenation step iscontinued and a further sample of the condensate is collected for thenext density measurement. Each sample is collected for a certain periodof time or until a certain volume is obtained.

So far, the invention has been described with respect to a batchoperation. However, the process of the invention can also be conductedcontinuously for example by using a reactor, like a rotating drumreactor or a screw reactor wherein the mixture comprising plastic and atleast one oxygenated compound is continuously moved from one reactionzone to the next. From each reaction zone, a gas stream is collected andthe density of the condensate of the gas stream is measured as describedabove. As long as the gas stream obtained from a given reaction zone hasa density of above about 0.94 g/cm³, the reaction zone is operated underdeoxygenation conditions. Once the mixture has moved into a reactionzone where the density of the condensate of the obtained gas stream isabout 0.94 g/cm³ or lower, this and the subsequent reaction zones areoperated under cracking conditions for obtaining product streamscontaining the desired gases, liquid fuels and waxes.

The gas stream obtained during the deoxygenation step contains gaseousproducts to which the oxygenated compounds are converted. By removingthis gas stream from the heated mixture, the oxygenated compounds areremoved and a residue mainly consisting of the plastic (and optionallythe above described unpyrolyzable components and small amounts ofplastic pyrolysis products) is obtained. This residue is subsequentlysubjected to cracking conditions.

It was furthermore found that the temperature at which oxygenatedcompounds are converted into gaseous products depends on the plastic inthe mixture. For example, oxygenated compounds are converted into gasesat a temperature slightly lower than 350° C. if the plastic ispolyethylene and at a temperature slightly lower than 300° C. if theplastic is polypropylene. This demonstrates that the plastic in themixture comprising plastic and the at least one oxygenated compoundinfluences the temperature at which the oxygenated compound is convertedinto gases.

As an important step of the process according to the invention the gasesproduced during the deoxygenation step are removed as a first gasstream. This gas stream contains the products of the undesiredoxygen-containing compounds which are thereby removed before the plasticis cracked. Removing of the first gas stream can for example beconducted by purging the space above the heated mixture with a gas, suchas air, preferably an inert gas, such as nitrogen. Alternatively oradditionally, the first gas stream can be removed by applying a reducedpressure.

In a preferred embodiment of the present invention, the gas streamobtained during the deoxygenation step is removed for a time sufficientto remove at least 50% by weight of the at least one oxygenated compoundfrom the mixture, based on the total weight of the at least oneoxygenated compound being present in the mixture prior to thedeoxygenation step. More preferably, at least 70% by weight, even morepreferably at least 80% by weight and most preferably substantially allof the at least one oxygenated compound is removed from the mixtureprior to the cracking step. In this context “substantially all of the atleast one oxygenated compound” is understood such that at least 90% byweight, preferably at least 95% by weight and even more preferably atleast 97% by weight based on the total weight of the at least oneoxygenated compound being present in the mixture prior to thedeoxygenation step is removed prior to the cracking step.

By removing the first gas stream from the heated mixture, a residue isobtained. This residue comprises the plastic which was not depolymerizedat the first temperature, optionally remaining amounts of oxygenatedcompounds, and optionally the above described unpyrolizable components.If the heating of the mixture at the first temperature has beenconducted in the presence of the catalyst, this catalyst is alsocomprised within the residue.

In the next step of the process according to the invention, the residueis submitted to cracking conditions. At these conditions, cracking ofthe plastic occurs thereby producing a product stream containing thedesired gases, liquid fuels and waxes. This product stream is removedfrom the heated residue.

Cracking of the plastic can be conducted under usual conditions known toa person skilled in the art. For example, the temperature duringcracking of the plastic usually is above 350° C., preferably above 400°C., more preferably at least 425° C., such as in the range of above 400°C. to 650° C., even more preferably in the range of 425° C. to 550° C.

In one embodiment, the cracking may be conducted in an air depletedatmosphere. An air depleted atmosphere can for examples contain orconsist of one or more inert gases, such as nitrogen, or can be atreduced pressure.

In a further embodiment, the cracking may be conducted in the presenceof a catalyst. It is, however, also possible that a catalyst is presentalso during the deoxygenation step. In this case, it is preferred thatthe deoxygenation step and the cracking step are conducted in thepresence of a catalyst, preferably the same catalyst. It is, however,also possible that the two steps are conducted in the presence of twodifferent catalysts or that a further, different catalyst is added tothe cracking step. Finally, it is possible, but less desired, that onlythe deoxygenation step is conducted in the presence of a catalyst,which, however, must then be removed prior to the cracking of theresidue.

The catalyst used in the process of the present invention can be anysuitable catalyst. Preferred catalysts are those used in FCC operationssuch as fresh FCC catalyst, spent FCC catalyst, equilibrated FCCcatalyst, BCA (bottom cracking additives) or any mixture thereof.

For example, the catalyst can comprise a zeolite-type catalyst. Suchcatalysts may be selected from crystalline microporous zeolites whichare known to the person skilled in the art and which are commerciallyavailable. Preferred examples for zeolite-type catalysts are describedin WO 2010/135273, the content of which is incorporated herein byreference. Specific examples for suitable zeolite-type catalysts includebut are not limited to ZSM-5, ZSM-11, ZSM-22, ZSM-23, ZSM-35, ZSM-48,ZSM-50, TS-1, TS-2, SSZ-46, MCM-22, MCM-49, FU-9, PSH-3, ITQ-1, EU-1,NU-10, silicalite-1, silicalite-2, boralite-C, boralite-D, BCA, andmixtures thereof. Alternatively or additionally, the catalyst maycomprise an amorphous-type catalyst which may comprise for examplesilica, alumina, kaolin, or any mixture thereof. Silica, in particularin the form of sand, is well known for FCC catalyst applications.

The skilled person is aware of suitable apparatus and equipment forcarrying out the process in accordance with the present invention and hewill select the suitable system based on his professional experience, sothat no further extensive details need to be given here.

Examples of suitable reactor types are fluidized bed, entrained bed,spouted bed, downcomer, fixed bed, rotating drum, rotating cone, screwcone, screw auger, extruder, molecular distillation, thin filmevaporator, kneader, cyclone and the like. Fluidized bed, entrained bed,spouted bed, screw auger and rotating drum are preferred. Screw augerand rotating drum are particularly preferred.

In one embodiment of the process according to the invention, thedeoxygenation step and the cracking step are conducted in two differentreactors.

In another embodiment of the process according to the invention, thedeoxygenation step and the cracking step are conducted in the samereactor. This can be done subsequently in the same section of a reactoror in two or more different sections of the same reactor, for example ina rotary drum or an auger where different sections are operated atdifferent temperatures.

The process according to the invention can be conducted batchwise,semi-batchwise or continuously. In the semi-batchwise mode, any feedstream and any product stream can be continuous but at least one feedstream or one product stream is discontinuous and/or at least one feedstream or one product stream is continuous.

The present invention furthermore relates to a process for removingoxygenated compounds from a mixture comprising plastic and at least oneoxygenated compound, the process comprises: heating the mixture to atemperature of at least 200° C. for a period until the condensate of thegas stream obtained from the heated mixture has a density of about 0.94g/cm³ or lower. In this process, the preferred embodiments are those asdescribed above.

Should the disclosure of any patents, patent applications, andpublications which are incorporated herein by reference conflict withthe description of the present application to the extent that it mayrender a term unclear, the present description shall take precedence.

The process of the present invention and its effects are now explainedin more detail with reference to the following examples.

The examples below were conducted according to the following generalexperimental procedure:

In each catalytic run in semibatch mode, 30 g of plastic (20%Polypropylene, 80% Polyethylene) were loaded inside the reactor and adefined amount of catalyst (approximately 20 g) was stored in thecatalyst storage tank. The reactor was closed and heated from roomtemperature to 200° C., while simultaneously purging with a 150 mL/minnitrogen flow. When the internal temperature reached the melting pointof the plastic, stirring was started and was slowly increased to 690rpm. The temperature was held at 200° C. for several minutes for plasticmelting and homogenization. During this heating process, nitrogen comingout from the reactor was collected in a gas sampling bag and nocondensates are recovered in the liquids traps. Meanwhile, the catalyststorage tank containing the catalyst was purged with nitrogen severaltimes.

After this first pretreatment step, temperature was increased to lessthan 425° C. at a heating rate of 10° C./min. During this time thecollection of gases and nitrogen was done in another gas sampling bag.Thereafter, the temperature was further increased to the crackingtemperature of 425° C. When the internal temperature reached thecracking temperature, the catalyst was introduced inside the reactor,and the circulation of the gaseous products was commuted to another pairof glass traps and corresponding gas sampling bag.

During selected time periods, liquid and gaseous products were collectedin a pair of glass traps and their associated gas sampling bag,respectively. At the end of the experiment the reactor was cooled toroom temperature. During this cooling step, liquids and gases were alsocollected.

The reaction products were classified into 3 groups: i) gases, ii)liquid hydrocarbons and iii) residue (waxy compounds, ashes and cokeaccumulated on the catalyst). Quantification of the gases was done bygas chromatography (GC) using nitrogen as the internal standard, whilequantification of liquids and residue was done by weight. Glass traps(along with their corresponding caps) were weighed before and after thecollection of liquids, while the reactor vessel was weighed before andafter each run.

The simulated distillation (SIM-DIS) GC method allowed determination ofthe different fractions in the liquid samples (according to the selectedcuts), the detailed hydrocarbon analysis (DHA) GC method allowsdetermination of the PIONAU (P: paraffins, I: iso-paraffins, =: olefins,N: naphthenes, A: aromatics, U: unidentified) components in the gasolinefraction of the last withdrawn sample (C5-C11: Boiling point<216.1° C.;what includes C5-C6 in the gas sample and C7-C11 in the liquid samples),and GCxGC allows the determination of saturates, mono-, di- andtri-aromatics in the diesel fraction of the last withdrawn liquidsamples (C12-C21; 216.1<BP<359° C.).

Depending on the source and purity of the plastic, two phase liquidsamples were obtained. In this case, THF was used as solvent in order toobtain a homogeneous liquid sample, and then SIM-DIS, DHA and GCxGC wasperformed. Besides, determination of the concentration of water in theseliquid THF-diluted samples was done by the Karl-Fischer titrationmethod.

In the examples, HCO refers to heavy cycle oil which is considered ashydrocarbon molecules with at least 22 carbon atoms (+C22). Waxes referto hydrocarbon molecules with at least 20 carbon atoms (+C20). Ingeneral:

-   -   Gasolines: contains C5s and C6s in gases +liquids with bp        (boiling point)<150° C. (ca. C5-C9)    -   Kerosene: liquids with boiling point 150<bp<250° C. (ca.        C10-C14)    -   Diesel: liquids with boiling point 250<bp<359° C. (ca. C15-C21)    -   HCO: products with boiling point>359° C. (C22 and +)    -   Waxes: products with boiling point>330° C. (C20 and +)

Determination of the different fractions is done by gas chromatographyby the simulated distillation method and according to the ASTM-D-2887standard.

Example 1

The experiment was carried out following the general procedure describedabove. Experiments were carried out using 80 wt % HDPE and 20 wt % PP(pure plastic that does not contain oxygenated compounds for comparisonin example 1.1 and plastic coming from a recycling plant and containingimpurities such as paper, metal foil, etc. in examples 1.2 and 1.3)preheated at ca. 105° C. to remove moisture as raw materials and 20 g ofan amorphous catalyst, namely SiO₂. Catalyst to dry plastic mixtureweight ratio was equal to 20/30 by wt. The results are summarized inTable 1 below.

Example 2

The experiment was carried out following the general procedure describedabove. Experiments were carried out using 80 wt % HDPE and 20 wt % PP(coming from a recycling plant and containing impurities such as paper,metal foil, etc.) preheated at ca. 105° C. to remove moisture as rawmaterials and 20 g of a equilibrated Fluidized Catalytic CrackingCatalyst (ECATDC) provided by Equilibrium Catalyst Inc. Catalyst to dryplastic mixture weight ratio was equal to 20/30 by wt. Three mixtures ofwaste HDPE and PP were prepared and submitted for catalyticdepolymerization (examples 2.1 and 2.2). The results are summarized inTable 1 below.

Example 3

The experiment was carried out following the general procedure describedabove. Experiments were carried out using 80 wt % HDPE and 20 wt % PP(coming from a recycling plant and containing impurities such as paper,metal foil, etc.) preheated at ca. 105° C. to remove moisture as rawmaterials and 20 g of a bottom cracking additive catalyst BCA-105provided by Johnson Matthey. Catalyst to dry plastic mixture weightratio was equal to 20/30 by wt (example 3.1). The results are summarizedin Table 1 below.

TABLE 1 Reaction Density of % H2O Reaction Temper- time Mass producedduring reaction time range (g) conden- removal Exam- Sam- time ature/range HCO Waxes sate at T < ple ple (min) ° C. (min-min) Gases GasolineKerosene Diesel (+C22) (+C20) H₂O TOTAL [g/cm³] 425° C. 1.1 #0 30.5200-425    0-30.5 0.14 0.15 0.11 0.05 0.02 0.03 0.48 0.782 #1 25 425 0-25 0.72 1.89 1.38 0.67 0.25 0.35 4.91 0.782 #2 40 425 25-40 0.27 0.710.78 0.64 0.04 0.10 2.44 0.786 #3 60 425 40-60 0.44 1.10 1.37 1.32 0.090.24 4.32 0.790 #4 90 425 60-90 0.66 1.68 2.29 3.98 1.71 2.78 10.300.822 1.2 #0 56 RT-425  0-56 0.82 0.17 0.21 0.12 0.04 0.05 2.02 3.380.947 89 #1 25 425  0-25 0.86 0.91 2.18 1.47 0.59 0.81 0.14 6.15 0.809#2 40 425 25-40 0.32 0.40 0.97 1.28 0.38 0.63 0.05 3.40 0.818 #3 60 42540-60 0.31 0.45 0.98 1.58 0.75 1.09 0.03 4.11 0.829 #4 90.5 425  60-90.50.19 0.19 0.41 0.99 1.12 1.40 0.03 2.93 0.865 1.3 #0 58 RT-425  0-580.85 0.19 0.24 0.09 0.10 0.10 1.97 3.43 0.944 91 #1 14 425  0-14 0.610.62 1.47 0.86 0.58 0.71 0.11 4.25 0.816 #2 34 425 14-34 0.44 0.58 1.251.52 0.45 0.75 0.04 4.28 0.815 #3 54 425 34-54 0.21 0.36 0.51 0.86 0.450.65 0.02 2.41 0.828 #4 75 425 54-75 0.15 0.27 0.38 0.74 0.56 0.74 0.022.10 0.841 2.1 #0 81.5 RT-425   0-81.5 1.63 0.22 0.17 0.07 0.03 0.031.84 3.96 0.944 85 #1 3.5 425  0-3.5 0.35 0.59 1.32 0.34 0.04 0.06 0.132.76 0.791 #2 8.5 425 3.5-8.5 0.32 0.54 1.36 0.61 0.07 0.12 0.09 2.990.795 #3 14.5 425  8.5-14.5 0.35 0.64 1.58 0.90 0.18 0.29 0.05 3.700.797 #4 23 425 14.5-23  0.39 0.63 1.35 0.96 0.31 0.44 0.04 3.68 0.8042.2 #0 64 RT-425  0-64 0.64 0.06 0.30 0.09 0.02 0.04 1.86 2.98 0.950 82#1 2.5 425  0-2.5 0.25 1.09 1.43 0.24 0.02 0.05 0.24 3.27 0.787 #2 6 4252.5-6  0.27 0.82 1.48 0.43 0.06 0.12 0.10 3.16 0.787 #3 11 425   6-11.00.26 0.70 0.87 0.38 0.10 0.16 0.04 2.36 0.788 #4 16 425  11-16.0 0.180.52 0.61 0.30 0.09 0.14 0.03 1.73 0.790 3.1 #0 55.3 RT-425   0-55.30.67 0.27 0.20 0.06 0.01 0.02 2.02 3.23 0.942 80 #1 9 425 0-9 0.49 0.670.79 0.27 0.07 0.12 0.36 2.65 0.811 #2 20 425   9-20.0 0.30 0.70 0.760.34 0.09 0.15 0.04 2.22 0.787 #3 33 425 20-33 0.29 0.64 0.96 0.68 0.170.28 0.05 2.79 0.798 #4 50 425 33-50 0.32 0.60 0.81 0.80 0.15 0.31 0.052.73 0.801 RT: room temperature

The data in the above Table 1 demonstrate that during the deoxygenationstep a major portion of the oxygenated compounds is removed from theplastic mixture (removal of the oxygenated compounds is determined bymeasurement of the water content in sample #0). On the other hand, theamount of water determined in the samples obtained in the cracking step(samples #1-#4) was only low. This demonstrates that the process of thepresent invention allows for the removal of oxygenated compounds from amixture comprising plastic and oxygenated compounds so that the gases,liquid fuels and waxes obtained by cracking contain only little oxygen.Simultaneously, only small amounts of plastic are cracked during thedeoxygenation step so that the overall yield of the desired gases,liquid fuels and waxes of low oxygen content is still good. Furthermore,a comparison of the products obtained in comparative examples 1.1 usingpure plastic that does not contain oxygenated compounds with theproducts of examples 1.2-3.1 demonstrates that removal of the undesiredoxygenated compounds prior to the cracking step does not significantlychange the product distribution.

1. A process for converting a mixture comprising plastic and at leastone oxygenated compound into gases, liquid fuels and waxes by cracking,the process comprising: a deoxygenation step which is conducted byheating the mixture to a temperature of at least 200° C. for a perioduntil the condensate of the gas stream obtained from the heated mixturehas a density of about 0.94 g/cm³ or lower; and subsequently to thedeoxygenation step a cracking step during which the mixture is subjectedto cracking conditions for obtaining a product stream containing saidgases, liquid fuels and waxes.
 2. The process according to claim 1,wherein the deoxygenation step is conducted until the condensate of thegas stream obtained from the heated mixture has a density in the rangeof 0.90 g/cm³ to 0.93 g/cm³.
 3. The process according to claim 1,wherein the temperature in the deoxygenation step is in the range of250° C. to 400° C.
 4. The process according to claim 1, wherein the gasstream obtained during the deoxygenation step and the product stream arekept separate from each other.
 5. The process according to claim 1,wherein the gas stream obtained in the deoxygenation step is removed fora time sufficient to remove at least 50% by weight, based on the totalweight of the at least one oxygenated compound being present in themixture prior to the deoxygenation step.
 6. The process according toclaim 1, wherein the plastic comprises waste plastic.
 7. The processaccording to claim 1, wherein the plastic comprises more than 50% byweight of polystyrene and/or polyolefin based on the total weight ofplastic.
 8. The process according to claim 1, wherein the cracking stepis conducted in the presence of a catalyst.
 9. The process according toclaim 8, wherein the deoxygenation step and the cracking step areconducted in the presence of a catalyst.
 10. The process according toclaim 8, wherein the catalyst is a zeolite-type catalyst and/or anamorphous-type catalyst.
 11. The process according to claim 8, whereinthe catalyst is fresh catalyst, equilibrated catalyst, or a mixturethereof.
 12. The process according to claim 1, wherein the deoxygenationstep and the cracking step are conducted in two different reactors. 13.The process according to claim 1, wherein the deoxygenation step and thecracking step are conducted in the same reactor.
 14. The processaccording to claim 1, which wherein the process is conducted batchwise,semi-batchwise or continuously.
 15. A process for removing oxygenatedcompounds from a mixture comprising plastic and at least one oxygenatedcompound, the process comprising: heating the mixture to a temperatureof at least 200° C. for a period until the condensate of the gas streamobtained from the heated mixture has a density of about 0.94 g/cm³ orlower.
 16. The process according to claim 2, wherein the deoxygenationstep is conducted until the condensate of the gas stream obtained fromthe heated mixture has a density in the range of 0.91 g/cm³ to 0.93g/cm³.
 17. The process according to claim 3, wherein the temperature inthe deoxygenation step is in the range of 250° C. to 380° C.
 18. Theprocess according to claim 5, wherein the gas stream obtained in thedeoxygenation step is removed for a time sufficient to remove at least70% by weight, based on the total weight of the at least one oxygenatedcompound being present in the mixture prior to the deoxygenation step.19. The process according to claim 6, wherein the plastic comprisesmixed waste plastic.
 20. The process according to claim 10, wherein thecatalyst is silica, alumina, kaolin, or a mixture thereof.